Sand core, coating apparatus and method for producing a sand core, in each case for the production of ventilated brake discs

ABSTRACT

A method for producing a sand core for the production of ventilated brake discs provides a sand body which has a circular and disc-shaped basic form and which has apertures. The apertures are arranged in circumferentially distributed fashion in the region of a ring of the circular and disc-shaped basic form. Subsequently, the sand body is partially coated with a liquid facing material, wherein the sand body is, in the region of a coating ring, washed around with the liquid facing material by way of a flooding process, wherein the coating ring covers the ring with the apertures, and wherein the apertures serve as flow ducts for the liquid facing material. Subsequently, the liquid facing material adhering to the sand body is dried. Also disclosed is a sand core and a coating apparatus for carrying out the partial coating of a sand body.

The invention relates to a method for producing a sand core for the production of ventilated brake discs, as per claim 1, to a sand core for the production of ventilated brake discs, according to claim 17, and to a coating apparatus for carrying out a partial coating of a sand body for the production of ventilated brake discs, according to claim 18.

Ventilated brake discs are composed of an (iron) casting with a circular and disc-shaped basic form, wherein a front disc, a rear disc and connecting elements, in particular webs, studs or pegs, between the front and rear discs are provided. Here, connecting webs normally extend from the inside outward in linear or curved fashion. Pegs are normally arranged in uniformly distributed fashion, in particular in a pattern. Here, the configuration of the webs, studs and pegs is extremely varied. Regardless of the specific configuration, ventilation chambers are arranged between the connecting elements in each case, which ventilation chambers are open at the inner circumference and at the outer circumference. Air can thus flow through the ventilation chambers.

To produce such ventilated brake discs, use is made of casting moulds. These normally have an upper mould, a lower mould and a lost sand core between the upper mould and the lower mould for forming the connecting elements and ventilation chambers. The casting moulds may be in the form of permanent moulds or in the form of lost (sand) moulds.

To achieve a high level of surface quality, the sand cores have not only a sand body but additionally a coating on the sand body. Said coating is applied by dipping the sand body into a basin with liquid facing material and is subsequently dried. During the drying process, the sand body is initially rotated and/or pivoted in order that no drip formations form. Here, some of the carrier liquid is absorbed into the sand core. The sand cores are subsequently dried in a furnace. Only a gripper region which is arranged in the centre of the sand body remains free from the coating of facing material. This is also achieved in particular by virtue of the disc-shaped sand body being only partially dipped into the basin and rotated about an axis of rotation which lies in the centre of the disc-shaped sand body.

A disadvantage of this method and the resulting sand core is that the coating exhibits low permeability to gases, which have to be discharged out of the casting mould during the casting process. If the casting gases cannot be discharged rapidly enough, internal or external gas inclusions form in the casting, in particular in the brake disc. This results in reject parts.

A further disadvantage of the prior art is the inhomogeneity of the facing material, which is in the form of a suspension, in the dip basin, said inhomogeneity resulting from the layering of constituents of different density. This results in an inhomogenous layer thickness of the coating on the sand body. This leads to low dimensional accuracy of the contour, formed by the core, of the castings or of the brake discs. Furthermore, the mounting of the casting core between the upper mould and lower mould can exhibit play or a bracing action resulting from the inhomogenous layer thickness in the connecting zone, in particular in the region of the core mark. An incorrectly positioned sand core likewise has an adverse effect on dimensional accuracy of the castings or of the brake discs.

Furthermore, the sand cores are stored when the coating has not yet fully dried, and leave facing material behind on the contact surfaces at the storage site. Said contact surfaces are normally delivery pallets. The storage site must therefore be regularly cleaned. Furthermore, during the detachment of the sand core from the storage site, damage can occur by virtue of a part of the sand core remaining adhered to the storage site.

Furthermore, during the dipping process, a relatively large volume of facing material can adhere to the sand body, and the costs for the facing material are correspondingly high.

It is therefore an object of the invention to eliminate the disadvantages of the prior art and provide a method for producing a sand core, a sand core, and an apparatus for carrying out the method for producing a sand core, by means of each of which, despite simple handling, high dimensional accuracy and surface quality of subsequent castings are attained, wherein the production costs for the sand core and the brake discs manufactured therewith are low.

Main features of the invention are specified in claims 1, 17 and 18. Claims 2 to 16 relate to refinements.

The invention relates to a method for producing a sand core for the production of ventilated brake discs, in which method, firstly, a sand core with a circular and disc-shaped basic form and with apertures is firstly provided, for example by shaping and compaction, wherein the apertures are arranged in circumferentially distributed fashion in the region of a ring of the circular and disc-shaped basic form. The sand body is subsequently partially coated with a liquid facing material, wherein the sand body is, in the region of a coating ring, washed around with the liquid facing material by way of a flooding process, wherein the coating ring covers the ring with the apertures, and wherein the apertures serve as flow ducts for the liquid facing material. The liquid facing material adhering to the sand body is subsequently dried.

An advantage of said method is that the facing material is in motion, whereby it exhibits a high level of homogeneity. Correspondingly, the layer thickness of the coating is more homogenous than in the case of a dipping process in a basin. As a facing material, use should be made of a suspension of ground and fireproof substances as base material and a fluid. This may comprise inter alia fireproof filler materials, a carrier liquid, binding agent and additives. The facing material is flowable and should be in a state between liquid and pasty. Water is preferably used as carrier liquid. Serving as a mould and core facing material of said type is the slurry of fine-grained or lamellar, fireproof filler materials with which sand moulds or sand cores are coated. The facing material functions, after a drying process, as a release agent and is intended to protect the mould and the core against thermal load and ferrostatic pressure, effect a good separation of the casting from the mould or from the core after the casting process, and at the same time positively influence the surface quality of castings.

By virtue of the fact that, by way of the flooding process, the coating ring can be defined on required coating regions, the volume of facing material consumed per sand core is low, and costs are low owing to the low consumption. Furthermore, partial regions of the sand core can remain non-coated, which partial regions consequently exhibit high permeability to gas. This results in a low reject rate in a process of casting brake discs using a sand core produced according to the invention, whereby the production costs per saleable brake disc are reduced.

The method is likewise suitable for sand bodies with circular, slot-shaped, straight or curved apertures.

A further advantage is that the non-coated regions of the sand core can be utilized as contact surfaces during the storage of the sand body. Thus, the storage site is not fouled with facing material, and the sand core does not adhere to the storage site. Owing to the smaller coating surface in relation to the prior art, it is also the case that less carrier liquid is absorbed into the sand core during the coating process and/or during the drying process. In this way, and owing to the fact that it is made easier for gas to escape, shorter drying times for the sand core are obtained.

The typically relatively high number of apertures for forming the subsequent connecting elements, for example connecting webs or connecting pegs, in a brake disc can permit a flooding process from only one direction of the sand body, because the facing material, after passing through the apertures, can also wet the rear side of the sand body. The facing material creeps, as it were, to a certain extent from the passage openings onto the rear side of the sand core before the flow separation from the sand body occurs. Flooding is however preferably performed from two sides, for example from two oppositely arranged outlet apparatuses, in order that the front side and the rear side of the coating ring are fully wetted.

In a more specific refinement of the method, it is provided that, owing to targeted guidance of the liquid facing material, a core mark which surrounds the ring with the apertures is not washed around during the partial coating of the sand body. Accordingly, gas can escape from the sand body and/or from the free space in the casting mould in the region of the core mark. Gas inclusions are thus prevented. Furthermore, the dimensional accuracy and the surface quality of brake discs manufactured using the sand core is high, because the non-coated core mark permits precise positioning on the lower mould and/or upper mould. Coated regions are preferably not in contact with other parts which form the mould cavity.

In one variant of the method, owing to targeted guidance of the liquid facing material, a centre region which is situated within the ring with the apertures is not washed around during the partial coating of the sand body. Said centre region is consequently also available for a good passage of gas.

Furthermore, a more specific refinement of the method provides that the apertures are of slot-shaped form and are closed at the end sides, and each extend (radially) from the inside outward with respect to the circular and disc-shaped basic form. With a sand body of said type, it is possible for webs to be produced between two discs. The slots may in this case be of straight, curved or evolvent-shaped form. Hole-like apertures, in particular oval or circular apertures, are optionally also conceivable. In this way, it is then the case during the casting process that studs, pegs or columns are produced between two discs of a disc brake.

In a particular specification of the method, the sand body is oriented (geodetically) horizontally during the partial coating with facing material, and a liquid flow of the facing material falls onto the sand body from above. By means of the falling height and the pressure of the facing material, the outlet speed can be adjusted such that the coating ring is uniformly wetted with facing material. In this case, facing material flows through the apertures.

In an alternative or additional embodiment, the sand body is oriented horizontally during the partial coating with facing material, and a liquid flow of the facing material impinges on the sand body from below. Any facing material of such an upwardly rising/spraying liquid flow which passes through the apertures from the bottom upward is conducted downward through the apertures again by the force of gravity. In this case, the delivery height of the second liquid flow should extend to a maximum of 15 cm above the brake disc in order to prevent spraying of the facing material out of the coating ring. It is optionally possible for a downwardly falling liquid flow and an upwardly flowing liquid flow to be provided simultaneously, by means of which the horizontally oriented sand body is impinged on from above and from below. In this case, the liquid flow falling from above flows onward in the downward direction through the apertures in the sand body.

In one embodiment of the method, the liquid flow of the facing material is dispensed from an outlet apparatus which has individual holes distributed over an area. In this way, the facing material volume that has to be delivered is low. Jets of facing material emerging from the holes are distributed over the sand body in the width direction owing to the impingement, such that the entire surface in the region of the coating ring is wetted. The individual holes are in this case preferably arranged parallel to one another in order to generate parallel jets of facing material. In particular in the edge region, however, it may be desirable for the jets of facing material to be angled, in particular directed inward, in order to be able to precisely wet the edges of the coating ring. Individual holes arranged so as to be distributed over the area are to be understood not exclusively to mean individual holes arranged in one plane. The individual holes may also be arranged with a height offset. It is furthermore not of importance whether the individual holes are formed into a common surface or are positioned using individual nozzles. The area of the individual holes is preferably assumed as an area projected perpendicularly with respect to the disc-shaped basic form. Because the wetting of the surface progresses even without a continuous impingement of facing material, it is advantageous, in order to reduce the volume of facing material to be delivered, if the area with the distributed individual holes amounts to at most 25%, preferably at most 20%, more preferably at most 15% and particularly preferably at most 13% of the area of the coating ring. The wetting of the entire coating ring is then realized by way of a relative (rotational) movement between the sand core and the outlet apparatus. Optionally, a second outlet apparatus may be provided for a second liquid flow which impinges from the opposite side. Said second outlet apparatus may be arranged oppositely or so as to be offset in the circumferential direction of the coating ring. An opposing arrangement is preferably selected in order that the delivery height of the second liquid flow is limited by the first liquid flow and, in this way, a dynamic pressure of the two colliding liquid flows is generated in the apertures. Particularly good wetting of the walls in the apertures is achieved in this way.

The costs of the method according to the invention are particularly low in a refinement in which a liquid circuit is formed during the flooding process, wherein the liquid facing material not adhering to the sand body is collected downstream of the sand body as viewed in the flow direction. The facing material can then be conducted or pumped back to the outlet apparatus directly or via an elevated tank. The optional use of an elevated tank is of particular advantage because the liquid facing material flows from an elevated tank to the sand body owing to the hydrostatic pressure. The flow speed can thus be very precisely defined and is uniform. The elevated tank and/or a collecting tank may have a circulating apparatus, for example a stirring mechanism.

The flooding of the sand body with facing material should be set such that at least 95%, preferably at least 97% and particularly preferably at least 98% of the liquid facing material not adhering to the sand body flows through the apertures during the flooding process. Spraying or running of facing material into regions outside the coating ring is thus prevented. Optionally, it is also possible for screens, templates, funnels or tubes to be used for targetedly channelling the facing material flow onto the coating ring.

One method refinement provides that the sand body is rotated horizontally while being washed around with liquid facing material. The rotation of the sand body has the effect that the facing material is distributed in a particularly effective manner. It is thus the case that all of the surfaces of the coating ring that are to be coated are reached, even on the rear side of the sand body. At the same time, facing material can fall vertically downward onto a small region of the coating ring. The rotation has the effect that the entire coating ring is gradually wetted. In this case, the sand body should perform at least one rotation, preferably multiple rotations, more preferably at most 15 rotations, particularly preferably at most seven rotations, for uniform wetting. It is also advantageous if the outlet apparatus can be arranged so as to be stationary, whereby the movement kinematics of the emerging facing material flow is easy to predict.

Furthermore, a method refinement is advantageous in which the sand body is rotated and/or pivoted during the drying of the (initially) liquid facing material. In this way, the facing material adhering to the sand body is distributed uniformly with a homogenous layer thickness, and no drip formations form. Furthermore, the movement in the air accelerates the drying of the facing material.

In a specific method variant, the sand body is, during the partial coating, mounted by way of a workpiece mount, which workpiece mount moves the sand body into a vertically falling liquid flow of liquid facing material, subsequently rotates the sand body in the liquid flow for a defined time period, preferably with a horizontal orientation of the sand core, and, after the flooding process, rotates and pivots the sand body for the purposes of drying the liquid facing material. The movements of the workpiece mount can thus be performed harmonically and in a definedly reproducible manner from the moment of initial contact with the liquid facing material to the drying thereof. In this way, it is possible for sand cores to be produced with uniform quality. For this purpose, the workpiece mount should be computer-controlled. Industrial robots are particularly suitable for the handling of the sand body.

A particular method refinement relates to the sand body which, in this case, has a ring-shaped first bevel, or is shaped and compacted with such a ring-shaped first bevel, wherein the first bevel is formed on the top side and/or on the bottom side of the circular and disc-shaped basic form, and wherein the first bevel radially surrounds the ring with the apertures. Such a first bevel/edge may in particular serve as a radial delimitation of the mould cavity in the casting mould. However, during the flooding process, the first bevel is of particular importance, because the coating ring can be delimited by way of a bevel of said type. A first bevel on the top side forms a flow barrier for the facing material. On the bottom side, a first bevel also serves in particular as a drip-off edge. That region of the sand body which is situated outside the first bevel is protected against wetting with facing material by the first bevel. At the same time, the first bevel leads to a precise boundary of the coating ring.

An optional further method refinement provides that the sand body has a ring-shaped second bevel, or is shaped and compacted with such a ring-shaped second bevel, wherein the second bevel is formed on the top side and/or on the bottom side of the circular and disc-shaped basic form, and wherein the ring with the apertures radially surrounds the second bevel. The advantages of such a second bevel substantially correspond to those of the first bevel, wherein, however, the centre and the workpiece holder are protected against wetting with facing material.

Furthermore, a more specific refinement relates to a method step in which the sand body has feet on the outer circumference of the circular and disc-shaped basic form, or is shaped and compacted with such feet. Said feet are expedient in particular in order to enable the sand mould to be set down on planar standard surfaces, without the facing material, which is still not completely dried, coming into contact with the storage site. Feet are also suitable for enabling multiple sand cores to be stacked one on top of the other. Furthermore, by means of feet, a free space is maintained around the coating with facing material, through which free space it is possible for air to circulate for the further drying process. Later in the casting tool, the feet serve in particular for precise positioning relative to further mould parts, in particular with regard to height, levelling and coaxiality with respect to the other mould parts.

The invention also relates to a sand core for the production of ventilated brake discs, having a sand body with a circular and disc-shaped basic form and with apertures, wherein the apertures are arranged in circumferentially distributed fashion in the region of a ring of the circular and disc-shaped basic form, wherein the sand body has a core mark which surrounds the ring with the apertures, wherein a coating is applied in the region of a coating ring of the sand body, wherein the coating is composed of a dried facing material, wherein the coating ring covers the ring with the apertures, and wherein at least 50%, preferably at least 70%, more preferably at least 85% and particularly preferably at least 90% of the surface of the core mark of the sand body is free from the coating.

An advantage of this is that the coating ring is defined on required coating regions; in particular, at least 50% of the core mark is non-coated, such that the required facing material volume per sand core is low, and the costs for the required facing material volume are low. In tests, it has been possible to achieve savings on facing material of up to 30%. Furthermore, the non-coated core mark exhibits high gas permeability. In this way, during casting of brake discs using a sand core produced in accordance with the invention, a low reject rate is achieved, whereby the manufacturing costs per saleable brake disc are low. The advantages described above in conjunction with the method also apply, at least in part, to the sand core according to the invention.

Optionally, the apertures may be of slot-shaped, straight, curved, evolvent-shaped or hole-shaped, in particular oval or circular, form. It is also possible for the sand core to have the further structural, material-specific and other features that have been described above in conjunction with the method.

The invention also relates to a coating apparatus for carrying out the partial coating of a sand body, as is performed in the context of the method described above, having a workpiece mount with a holding means for holding the sand body, a holding arm for moving the sand body in space, and a rotary drive for rotating the sand body. Furthermore, the coating apparatus comprises an elevated tank for storing liquid facing material, an outlet apparatus which is arranged below the elevated tank and is connected in terms of flow to the latter, a collecting tank below the outlet apparatus, and a return delivery line with pump between the collecting tank and the elevated tank.

An advantage of a coating apparatus designed in this way is that a sand body can be uniformly partially wetted with facing material by virtue of the sand body being rotated in space below the outlet apparatus. By means of the arm, the feed and storage of sand bodies can be performed in fully automated fashion, and furthermore, the wetted sand body can be moved in a defined movement profile for the purposes of drying the facing material. In this way, the facing material can be distributed in such a way that no drip formations or inhomogeneities form in the coating.

In practice, outlet apparatuses with exchangeable and/or variable-length nozzle rows have proven to be particularly expedient.

The coating apparatus may also have the further structural, material-specific and other features that have been described above in conjunction with the method. The advantage of the elevated tank is a constant volume flow with little technical outlay. Instead of the elevated tank, it is however also conceivable to provide a direct connection between the pump and the outlet apparatus, in particular if the pump is set up for constant delivery of the facing material, for example by being equipped with regulation technology.

Further features, details and advantages of the invention will emerge from the wording of the claims and from the following description of exemplary embodiments on the basis of the drawings, in which:

FIG. 1 shows a perspective view of a sand core;

FIG. 2 shows a cross section through a casting mould with a sand core;

FIG. 3 shows a perspective view of a ventilated brake disc;

FIG. 4 shows a perspective view, including a partial section, of another ventilated brake disc;

FIG. 5 shows a schematic view of a coating apparatus, with a sand core being flooded with facing material; and

FIG. 6 shows a schematic view of a coating apparatus, with a sand core being dried outside a liquid flow.

FIG. 1 shows a sand core 1 for the production of ventilated brake discs. Said sand core has a sand body 10 with a circular and disc-shaped basic form 11 with a top side S1 and a bottom side S2. In the circular and disc-shaped basic form 11 there are formed apertures 12, which in this case are optionally slot-shaped, between the top side S1 and the bottom side S2, which apertures are arranged in circumferentially distributed fashion in the region of a ring 13 of the circular and disc-shaped basic form 11. Furthermore, the slot-shaped apertures 12 are in each case closed at the end sides and extend in each case from the inside outward. Furthermore, the sand body 10 has a core mark 14 which surrounds the ring 13 with the apertures 12.

In the region of a coating ring 31 of the sand body 10, a coating has been applied, wherein the coating is composed of a dried facing material 30. The coating ring 31 is slightly wider than the ring 13 with the apertures 12 and covers the latter. Thus, the entire ring 13 with the apertures 12 is coated with facing material 30.

In this case, more than 50% of the surface of the core mark 14 of the sand body 10 is free from the coating with facing material 30. The sand body 10 furthermore has feet 18 which are arranged on the outer circumference of the circular and disc-shaped basic form 11, which feet are likewise substantially free from facing material 30; in particular, more than 80% of said feet are free from facing material.

In the present exemplary embodiment, it can be seen that individual strips of facing material 30 have passed onto the core mark 14, in particular as a result of the rotation of the sand body 10. This can however be optimized through adjustment of the process parameters during the coating and drying processes, in particular also by way of optimization of bevels 16, 17 on the top side S1 and on the bottom side S2.

As can be seen, the sand body 10 has a ring-shaped first bevel 16 on the top side S1 of the circular and disc-shaped basic form 11. Said first bevel 16 radially surrounds the ring 13 with the apertures 12. Also formed on the top side S1 is a ring-shaped second bevel 17. Said second bevel 17 is radially surrounded by the ring 13 with the apertures 12. The bevels 16, 17 thus in each case form an elevation relative to the coating ring 31 and also relative to the ring 13 with the apertures 12. Within the second bevel 17 and thus also within the ring 13 with the apertures 12 there is situated a centre region 15 which is likewise not coated with facing material 30. Said centre region 15 serves in particular for the attachment of holders or grippers during the individual process steps.

In the case of the sand core 1 that is shown, gas can escape from the sand body 10 during casting of a brake disc through the non-coated regions of the sand body 10, specifically the core mark 14, the feet 18 and the centre region 15.

With a sand core 1 of such type or of similar type, it is possible to manufacture brake discs with a high surface quality and dimensional accuracy. For this purpose a sand core 1, as illustrated in a cross section through a casting mould 300 in FIG. 2, is placed into a free space between an upper shell 301 and a lower shell 302. The free space, which is reduced in size by the sand core 1, forms a mould cavity 303 for liquid melt. In the present case, the mould cavity has previously been filled with cast iron, such that a brake disc 100 has been formed. Gate and ventilation openings and the like in this case do not lie in the section of the casting mould, but should be planned into the design thereof. The upper and lower shells 301, 302 may be composed of permanent moulds and/or lost moulds. A design composed of more than two parts is also possible. The statements relating to FIG. 1 apply to those reference signs that are not explicitly discussed with regard to FIG. 2.

For example, with a casting mould 300 as per FIG. 2 or a similar casting mould, it is possible to manufacture brake discs 100 such as are shown by way of example in a perspective view in FIGS. 3 and 4. The brake discs 100 as per FIGS. 3 and 4 each have a circular and disc-shaped basic form, wherein a front disc 101, a rear disc 102 and connecting elements or connecting webs 103 between the front and the rear disc 101, 102 are provided. Here, the connecting webs 103 extend linearly in FIG. 3 and extend in curved fashion from the inside to the outside in FIG. 4. Between the connecting webs 103 there are arranged ventilation chambers 104 which are formed so as to be open at the inner circumference and at the outer circumference. It is thus possible for air to flow through the ventilation chambers 104. Such ventilated brake discs 100 are normally composed of a cast-iron part.

FIG. 5 shows a schematic view of a coating apparatus 200 for carrying out a partial coating of a sand body 10. It is possible to see a workpiece mount 201 with a holding means 202 for holding the sand body 10. The sand body 10 is shown in section and has a circular and disc-shaped basic form 11 and slot-shaped apertures, wherein the apertures are arranged in circumferentially distributed fashion in the region of a ring 13 of the circular and disc-shaped basic form 11, are in each case closed at the end sides, and each extend from the inside outward. The sand body 10 may be designed as in FIG. 1.

A core mark 14 of the sand body 10 radially surrounds the ring 13 with the apertures 12. In this case, feet 18 are attached to the core mark 14, which feet are oriented transversely, in particular perpendicularly, with respect to the circular and disc-shaped basic form 11. In the direction of the image, that is to say also geodetically, the feet 18 point downward.

Within the ring 13 with the apertures 12, there is situated a centre region 15 of the sand body 10. The holding means 202 of the coating apparatus 200 engage on said centre region. The workpiece mount 201 has a rotary drive by means of which the holding means 202 and the sand body 10 are rotatable about an axis of rotation. The axis of rotation may in this case be oriented geodetically vertically. It can be seen that the workpiece mount 201 is mounted on a holding arm 209, which in this case is in particular formed with three members. Said holding arm 209 may be part of an industrial robot. It is consequently possible for the sand body 10 to be moved in space and rotated about the axis of rotation.

Furthermore, the coating apparatus 200 has an elevated tank 203 in which liquid facing material 30 is stored. Below the elevated tank 203 there is arranged an outlet apparatus 205 which is connected in terms of flow to the elevated tank 203. The outlet apparatus 205 has individual holes 206 distributed over an area, similarly to a shower head or a nozzle row. The individual holes 206 are oriented downward.

In addition or optionally, a second outlet apparatus 210 is provided. Said second outlet apparatus 210 is connected in terms of flow to the elevated tank 203. Furthermore, the second outlet apparatus 210 has individual holes 211 distributed over an area, similarly to a shower head or a nozzle row. The second outlet apparatus 210 is positioned below the sand core 10 and is designed for an upward outflow of facing material 30; in particular, the individual holes 211 point upward.

It is optionally possible for flow to be supplied to the individual holes 206, 211 in each case via individual lines. In this case, a separation into the individual lines should preferably be realized in a downwardly falling line section or directly at the elevated tank 203. This prevents solid particles of the suspension from accumulating in corners of the feed line and possibly abruptly re-entering the flow in the form of lumps. The facing material 30, which is in the form of a suspension, thus flows homogenously out of all of the individual holes 206, 211.

For collecting facing material 30, a collecting tank 204 is provided below the outlet apparatus 205. A fluid circuit for the facing material 30 is formed by way of a return delivery line 207 with a pump 208 which is arranged between the collecting tank 204 and the elevated tank 203. A constant volume flow of the facing material is realized by way of the elevated tank 203. It is optionally also possible for the pump 208 to be connected directly to the outlet apparatus.

The coating apparatus 200 is suitable for carrying out a coating process in which the sand body 10 is partially coated. Only regions of the sand body 10 situated below and/or above the outlet apparatus 205, plus an area of scatter, are wetted with facing material 30 if the sand body 10 is oriented horizontally and a liquid flow of the facing material 30 impinges on the sand body 10 from above and/or from below. It can be seen that the sand body 10 is washed around with the liquid facing material 30 by way of a flooding process only in the region of a coating ring 31. In order that the entire coating ring 31 is wetted, it is provided that the sand body 10 is rotated horizontally as it is washed around with liquid facing material 30.

The coating ring 31 completely overlaps the ring 13 with the slot-shaped apertures. The downwardly falling facing material 30 thus wets a part of the top side S1, before the excess, non-adhering facing material 30 flows through the slot-shaped apertures. Facing material 30 which penetrates through the apertures from below is conducted downward again through the apertures owing to gravitational force. The apertures consequently serve as flow ducts for the liquid facing material 30. In this case, the facing material 30 at least partially remains adhered to the sand body 10. The remaining part either flows directly through the apertures or drips/flows off the sand body 10. Below the sand body 10, said part of the facing material 30 is collected in the collecting basin 204.

By virtue of the outlet apparatuses 205, 210 above and/or below the sand core 10 being offset inward, it is achieved that a core mark 14 surrounding the ring 13 with the apertures 12 is not washed around during the partial coating of the sand body 10. Also, owing to targeted guidance of the liquid facing material 30, a centre region 15 situated within the ring 13 with the apertures is not washed around with said facing material.

For the drying of the liquid facing material 30 adhering to the sand body 10, the sand body 10 is rotated and/or pivoted by means of the holding arm 209 and the workpiece mount 201, either after an interruption of the flow of facing material 30 or, as shown in FIG. 6, outside the flow of facing material 30. In this case, excess facing material 30 drips into the collecting basin 204. The rest of the facing material 30 dries as a result of extraction of the carrier liquid, in particular as a result of absorption of the carrier liquid into the sand body 10. A sand core 1 according to the invention is finally formed. Before the use of the sand core, the latter is subjected to further drying, in particular in a furnace, in order to expel moisture from the interior of the sand core.

The invention is not restricted to one of the above-described embodiments, but may be modified in a variety of ways.

Inter alia, it is for example possible for the outlet apparatuses 205, 210 to be positioned closer to the sand core than is illustrated in the schematic sketches in FIGS. 5 and 6. It is also possible for additional screens and templates to be used to channel the facing material to particular regions of the sand core 10. It is however preferably possible to dispense with this, in particular if permitted in technical terms by the geometry of the casting or of the brake disc.

All of the features and advantages that emerge from the claims, from the description and from the drawing, including structural details, spatial arrangements and method steps, may be essential to the invention both individually and in a wide variety of combinations.

LIST OF REFERENCE SIGNS

-   1 Sand core 200 Coating apparatus -   201 Workpiece mount -   10 Sand body 202 Holding means -   Circular and disc-shaped basic 203 Elevated tank form 204 Collecting     tank -   12 Aperture 205 Outlet apparatus -   13 Ring 206 Individual hole -   14 Core mark 207 Return delivery line -   15 Centre region 208 Pump -   16 First bevel 209 Holding arm -   17 Second bevel 210 Second outlet apparatus -   18 Foot 211 Second individual holes -   30 Facing material 300 Casting mould -   31 Coating ring 301 Upper shell -   302 Lower shell -   100 Brake disc 303 Mould cavity -   101 Front disc -   102 Rear disc S1 Top side (basic form) -   103 Connecting element/web S2 Lower side (basic form) -   104 Ventilation hole 

1. Method for producing a sand core (1) for the production of ventilated brake discs (100), comprising the steps: providing a sand body (10) which has a circular and disc-shaped basic form (11) and which has apertures (12), wherein the apertures (12) are arranged in circumferentially distributed fashion in the region of a ring (13) of the circular and disc-shaped basic form (11); partially coating the sand body (10) with a liquid facing material (30), wherein the sand body (10) is, in the region of a coating ring (31), washed around with the liquid facing material (30) by way of a flooding process, wherein the coating ring (31) covers the ring (13) with the apertures (12), and wherein the apertures (12) serve as flow ducts for the liquid facing material (30); drying the liquid facing material (30) adhering to the sand body (10).
 2. Method according to claim 1, characterized in that, owing to targeted guidance of the liquid facing material (30), a core mark (14) which surrounds the ring (13) with the apertures (12) is not washed around during the partial coating of the sand body (10).
 3. Method according to claim 1, characterized in that, owing to targeted guidance of the liquid facing material (30), a centre region (15) which is situated within the ring (13) with the apertures (12) is not washed around during the partial coating of the sand body (10).
 4. Method according to claim 1, characterized in that the apertures (12) are of slot-shaped form and are closed at the end sides, and each extend from the inside outward with respect to the circular and disc-shaped basic form (11).
 5. Method according to claim 1, characterized in that the sand body (10) is oriented horizontally during the partial coating with facing material (30), and a liquid flow of the facing material (30) falls onto the sand body (10) from above.
 6. Method according to claim 1, characterized in that the sand body (10) is oriented horizontally during the partial coating with facing material (30), and a liquid flow of the facing material (30) impinges on the sand body (10) from below.
 7. Method according to claim 4, characterized in that the liquid flow of the facing material (30) is dispensed from an outlet apparatus (205, 210) which has individual holes (206, 211) distributed over an area.
 8. Method according to claim 1, characterized in that a liquid circuit is formed during the flooding process, wherein the liquid facing material (30) not adhering to the sand body (10) is collected downstream of the sand body (10) as viewed in the flow direction.
 9. Method according to claim 1, characterized in that the liquid facing material (30) flows to the sand body (10) from an elevated tank (203).
 10. Method according to claim 1, characterized in that at least 95% of the liquid facing material (30) not adhering to the sand body (10) flows through the apertures (12) during the flooding process.
 11. Method according to claim 1, characterized in that the sand body (10) is rotated horizontally while being washed around with liquid facing material (30).
 12. Method according to claim 1, characterized in that the sand body (10) is rotated and/or pivoted during the drying of the liquid facing material (30).
 13. Method according to claim 1, characterized in that the sand body (10) is, during the partial coating, mounted by way of a workpiece mount (201), which workpiece mount moves the sand body (10) into a vertically falling liquid flow of liquid facing material (30), subsequently rotates the sand body in the liquid flow for a defined time period, and, after the flooding process, rotates and/or pivots the sand body (10) for the purposes of drying the liquid facing material (30).
 14. Method according to claim 1, characterized in that the sand body (10) has a ring-shaped first bevel (16), wherein the first bevel (16) is formed on the top side (S1) and/or on the bottom side (S2) of the circular and disc-shaped basic form (11), and wherein the first bevel (16) radially surrounds the ring (13) with the apertures (12).
 15. Method according to claim 1, characterized in that the sand body (10) has a ring-shaped second bevel (17), wherein the second bevel (17) is formed on the top side (S1) and/or on the bottom side (S2) of the circular and disc-shaped basic form (11), and wherein the ring (13) with the apertures (12) radially surrounds the second bevel (17).
 16. Method according to claim 1, characterized in that the sand body (10) has feet (18) on the outer circumference of the circular and disc-shaped basic form (11).
 17. Sand core (1) for the production of ventilated brake discs (100), having a sand body (10) with a circular and disc-shaped basic form (11) and with apertures (12), wherein the apertures (12) are arranged in circumferentially distributed fashion in the region of a ring (13) of the circular and disc-shaped basic form (11), and wherein the sand body (10) has a core mark (14) which surrounds the ring (13) with the apertures (12), characterized in that a coating is applied in the region of a coating ring (31) of the sand body (10), wherein the coating is composed of a dried facing material (30), wherein the coating ring (31) covers the ring (13) with the apertures (12), and wherein at least 50% of the surface of the core mark (14) of the sand body (10) is free from the coating.
 18. Coating apparatus (200) for carrying out the partial coating of a sand body (10) as per a method according to claim 1, having: a workpiece mount (201) with a holding means (202) for holding the sand body (10), a holding arm (209) for moving the sand body (10) in space, and a rotary drive for rotating the sand body (10); an elevated tank (203) for storing liquid facing material (30); an outlet apparatus (205, 210) which is arranged below the elevated tank (203) and is connected in terms of flow to the latter; a collecting tank (204) below the outlet apparatus (205, 210); and a return delivery line (207) with pump (208) between the collecting tank (204) and the elevated tank (203). 